I very much doubt the import process will keep the same id's for users/posts/threads therefore I am quite sure you will have problems.
I would analyse your server logs / analytics for the most popular threads and manually create a few re-write rules.
Hopefully (big ask) xenforo will record 'old' id's in the import process and may provide a way to redirect old original urls to new urls although everyone with vBseo will need to create some nifty re-write rules.
Does anybody in the xF team have anything to say on this topic?
Given our background, we have a fully-armed and operational vBulletin 3.x importer ready. We also have a tool that you can deploy that will catch links destined for forums, threads, posts etc. from your old board and redirect them (with a 301) to the newly-imported XenForo versions, [...]